Manufacture of spark plugs



June 13, 1939. D. H. CORBIN MANUFACTURE OF SPARK PLUGS 7 Filed March 17,1958 Fig. '1.

Patented June 13, 1939 UNITED STATES MANUFACTURE OF SPARK PLUGS DouglasHaynes Corbin, Dunstable, England, as-

signor to General Motors Corporation, Detroit, Mich, a corporation ofDelaware Application March 17, 1938, Serial No. 196,309 In Great BritainMarch 19, 1937 11 Claims.

This invention relates to the manufacture of spark plugs for internalcombustion engines.

The object of the invention is to provide a simple and effective processof manufacturing a high efficiency spark plug.

According to the invention, which in its various aspects is indicated inthe appended claims, a spark plug is made by positioning an electrode ofcorrosion-resisting material on or in the insulator, and it is themfirmly attached thereto by introducing a metal into the central bore ofthe insulator in such a manner that it contacts with a part of theelectrode in a molten state, and then cooling the metal.

Good heat conductivity metals having a comparatively low melting pointsuch as copperand silver may be used for the central bore: it forms theconducting portion of the central electrode and therefore of courseshould have a melting point such that it will not be adversely affectedunder operating conditions.

The sparking portion of the central electrode is made ofcorrosion-resisting material, and for this nickel-chrome alloys may beused although platinum and platinum alloys. are preferred.Platinum-rhodium, platinum-indium, and pure platinum indicates the orderof preference.

Further features of the invention will be apparent from the followingdescription taken in conjunction with the accompanying drawing in which:

Figure 1 is a part section of a spark! plug having parts made accordingto this invention; and

Figures 2 to 7 illustrate various forms of electrode and insulatorassemblies.

The same reference characters indicate like parts in the variousfigures.

The form of spark plug shown in Figure 1 is merely illustrative of theinvention which can be appiied to many different forms of plugs. Theparticular form shown therefore need not be de scribed in detail, and itis sufficient to indicate the structure as comprising an outerscrew-threaded shell a, an inner shield member b having an innerinsulating lining c, and an inner sleeve d holding the central insulatore. This latter extends inside the lining c and carries a connecting capI for connecting a spring (not shown) to the central electrode structureformed of a screwed-in member 9, a central conducting piece h andsparking electrode points i which cooperate with a ring of nickel orplatinum alloyon the inside of the shell a.

In the preferred embodiment the insulator e (Cl. l23169) is made of ahighlymefractory oxide or oxides sintered into a dense mass, theelectrode conducting piece 12 is made of silver, and the points i aremade of fine wires of platinum-rhodium alloy. The tip of the insulatorassembly is shown in Figure 2.' v

The manner of making this assembly is as follows:

The insulator e is made with a central bore and with a plurality ofcommunicating divergent channels of just sufiicient size to permit theinsertion of the fine wires 1' as shown in Figures 1 and 2. Prior toinsertion the ends of the wires which are to project into the centralbore are plated with chromium and then heated to a red heat 15 to form aprotective coating. The end tip of each wire is then nipped off, and thewires are inserted in their respective channels so as to project intothe central bore. To help hold the wires in po-'- sition during thecasting process, and also to stop any silver from running down betweenthe wires and the sides of the hole, the wires and the end of theinsulator are sealed off with a protective ceramic cement, which has amelting point higher than the fusing point of the metal used forsealing, yet with enough adhesion to hold the wires in place. The silveris then introduced into the bore in such a manner as to contact with theends of the wires in a molten condition. This may be done bypouringmolten silver intothe bore but the preferred method is toaplace a pieceof'solid silver in the bore and then heat the whole. assembly to atemperature sumcient to melt the silver. This heating may be effected inair, or in a vacuum or in an inert atmosphere.

The assembly is then allowed to cool and in so doing the silver mouldsitself to the bore and also firmly retains the wires in position. Thereis a fused connection between the silver and the wire at the unprotectedsurface of the latter.

The constructions shown in the remaining Figures 3 to 7 are made in asimilar manner.

In Figure 3 the sparking electrode is formed as a cylindrical cap itcrimped over the tip of the insulator e, and the silver is in contacttherewith 45 through a plurality of channel pieces I.

The construction of Figure 4 is obviously a modification of that inFigures 1 and 2.

In the form shown in Figure 5 cylindrical cap is fits directly into theend of the central bore 50 and is retained therein by set silver.

In the form shown in Figure 6 the sparking electrode is made in thegeneral form of a cylindrical cap 9' which is crimped onto the end ofthe insulator, and is provided with a plurality of pro- .55

iectlons m forming the sparking points. Between the bore and the cap I:are a plurality of communicating channeLpieces 1 formed when the silveris in the molten condition.

In a further form shown in Figure 7 the sparking electrode is made inthe form of a star memher 1: having a central dished portion which fitsinto the end of the bore and which forms in elect a key with the silvertherein.

In all the forms shown in Figures 3 and 5 to 'i the sparking electrodepiece may be treated to form a protective coating except where fusion Iwith the silver is required, similarly to the treatment of the finewires, above described. Thus. according to the invention, the usualcentral electrode takes the form of a cast or moulded metal piece, andthis piece not only acts as the conductor, but also as the retaining andfixing means for the sparking electrode positioned at the end of theinsulator.

1. A method of making a spark plug having an insulator with a centralbore and an electrode which comprises positioning on the insulator anelectrode made of a platinum alloy so as tobe in communication with thecentral bore, introducing silver into the bore and. bringing it intocontact with said electrode whilst in a molten state. then letting thesilver cool so as to retain the electrode in position.

2. A method of making a spark plug which comprises forming an insulatorwith a central bore, and a pluralityof communicating bores at theend-thereof, positioning at the end of the insulator an electrode membermade of a platinum alloy so as to be in part within one of the bores,introducingsilver into the central bore so as to contact with theelectrode in a molten state, and then cooling the silver so as to retainthe electrode in position.

3. A method of making a spark plug which comprises forming an insulatorwith a central bore, and a plurality of communicating bores at the endthereof, fitting at the end of the insulator an electrode member ofcylindrical form and made of a platinum alloy soas to be in part incommunication with the bores, introducing silver into the central boreso as to contact at the ends of the communicating bores with theelectrode in a molten state, and then cooling the silver so as to retainthe electrode in position. 4. A method of making a spark plug whichcomprises forming an insulator with a central bore and with a pluralityof fine channels at the tip thereof, communicating with the bore,inserting a fine wire electrode in each of the channels so as to projecttherefrom at each end, introducing a metal-into the bore so as to bringit into contact in a molten state, with the ends of the fine wires inthe bore, and then cooling the metal to retain the wires in position.

5. A method of making a spark plug which comprises forming an insulator.with a central bore and with a plurality of fine channels at the tipthereof, communicating with the bore forming a protective coating on aplurality of fine wires inserting one of said fine wires in each of thechannels so as to project therefrom at each end, introducing a metalinto the bore so as to bring it into contact in. a molten state with theends oi the fine wires in the bore so as to form a fused connectionbetween them and the molten metal over only a limited area, and thencooling the metal to retain the wires in position.

6. A method of making a spark plug which comprises forming an insulatorwith a central bore and with a plurality of fine channels at the tipthereof, communicating with the bore forming a protective coating on aplurality of fine wires of a platinum alloy inserting one of said finewires in each of the channels so as to project therefrom at each end,introducing silver into the bore so as to bring it into contact in amolten state with the ends of the iine wires in the bore, tov form afused connection between them and the molten silver over only a limitedarea, and then cooling the silver to retain the wires in position.

insulator with a central bore, which comprises fitting the electrodeinto the end of the central bore so as to project in part therefrom,introducing silver into the bore and bringing it into contact with saidelectrode whilst in a molten state, then letting the silver cool so asto retain the electrode in position.

8. A method of making a spark plug having an insulator with a centralbore which comprises fitting on the insulator an electrode ofcorrosionresisting material in the form of a star-shaped member having acentral portion, so that said portion fits in said central bore,introducing siliver into the bore and bringing it into contact with saidcentral portion whilst in a molten state,

then letting the silver cool so as to retain the trode fitted at the tipof the insulator in fused connection with the silver in thecentral-bore. 10. A spark plug comprising an insulator formed of ahighly refractory oxide, a central bore and communicating channels inthe tip of said insulaton'said bore being filled with silver, and aplurality of fine wire platinum alloy electrodes fitted in said channelsin fused connection at their inner ends with the silver'in the centralbore.

11. A spark plug'comprising an insulator having a longitudinal boretherein, anelectrode tip of metal resistant to heat and corrosion fittedto the lower end 'of the plug and extending a short distance only intothe lower end of the bore, the

DOUGLAS HAYNES connm."

